Tuesday, 20 May 2014

Species of the month: Bittern

Ed Parnell of Norfolk Wildlife Trust

Visit some of the larger reedbeds of the Broads in May, particularly early in the morning or around dusk, and there’s every chance you’ll hear a strange booming sound, reminiscent of someone blowing across the top of an empty bottle: the breeding call of the male bittern, one of the UK’s rarest and most unusual birds.

Bittern, photo by Ed Parnell
The bittern is a member of the heron family, but differs widely in its plumage from the commonly-encountered grey heron. Bitterns have a light, straw coloured base colour, which is exotically streaked with darker, almost-black, lines and chevrons. The overall effect is exceptionally cryptic and it is little wonder that the bird blends so effortlessly into its favoured reedbed habitat. Although bitterns have a long neck, which they stretch out vertically to mimic their surroundings when alarmed, they never appear as tall and elegant as herons. Indeed, in certain poses they almost seem to take on a rather hunched, owl-like appearance. What never changes is the lethal dagger-like bill, which is used to impale unfortunate frogs, fish and small mammals with lethal precision.

As to the bittern’s boom, this remarkable sound is produced when the courting male bird exhales air from its oesophagus. The noise, usually repeated in short sequences of three or four chimes, has the lowest frequency of any note produced by a British bird and can be heard from up to three miles away.

Bitterns were a common bird in medieval times, when wetland and reedbed in places like the Fens was much more prevalent. They were also considered a great delicacy for the table and eaten in large numbers (sometimes hundreds at a time) at medieval banquets. Over-hunting, along with the loss of its habitat, factored in its decline and by the end of the Victorian age, the species had disappeared as a British breeding bird.

Bittern in the reeds, photo by Liz Dack
So when in 1911 the Edwardian naturalist Emma Turner photographed a nestling at Hickling Broad, there was much excitement. And despite a gradual increase in numbers over the following decades (with Norfolk the UK stronghold), the species began a severe downward spiral in the late 1960s. By 2010 the UK population contained just 14 booming male birds.

However, dedicated conservation work (including generous EU funding) has helped to turn things around so that in 2011 the UK population of the species reached 104 males, with 23 of these in Norfolk. These are centred around the Broads, with smaller numbers in suitable habitat along the north Norfolk coast at sites such as NWT Cley Marshes and NWT Holme Dunes. The best places to hear the species though (for they are very hard to see, unless you happen to be in the right place at the right time) is in the Broads, with NWT Hickling Broad offering a very good chance.

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